A rare and primitive fish, famed as a "living fossil" unchanged for millions of years, has been found in the deep waters off a remote Indonesian island, nearly 6,000 miles away from its only known habitat.

Discovery of a population of the fish so far from its known home has astonished biologists, to whom it poses a fascinating puzzle in the evolution and spread of a species. According to fossil records, the fish must have thrived more than 350 million years ago - and today appears exactly like its ancient forebears.The oily, ugly creature with its snapping teeth and lobe-shaped fins is a coelacanth (see-la-kanth), and scientists long thought it had been extinct for at least 65 million years - until the first living example of its kind was caught off the coast of East Africa 60 years ago.

Since then, the coelacanth has been found only around the Comoro Islands in the Indian Ocean, with a few strays from the Comoros caught off Madagascar. It is so rare that it is protected as an endangered species by international treaty.

But that hasn't protected the deep-water denizen from the nets of fishermen, who catch it and sell it dried and salted in outdoor markets.

A year ago, Arnaz Mehta, the wife of a biologist at the University of California at Berkeley, spotted one lying dead in a fish market in the town of Manado on the northeast peninsula of Indonesia's Sulawesi mainland. Her husband, Mark V. Erdmann, is studying shrimp species there as a key to the ecology of the region's abundant but threatened coral reefs.

With support from the National Geographic Society, Erdmann quickly surveyed local fishermen about what they knew of the curious fish they called "king of the sea," and last July, the crew of one fishing vessel brought him a live specimen netted off the tiny Sulawesi island of Manadotua. It was more than four feet long and weighed nearly 65 pounds.

Erdmann quickly extracted a small tissue sample from the fish, then preserved it temporarily in a deep-freeze. The importance of the find is "enormous," he said in an e-mail message to his Berkeley colleagues, and added: "It is a humbling and exciting reminder that humans have by no means conquered the oceans, and provides fodder for our imagination about other, as-yet-undiscovered `sea monsters.' It underscores the importance of protecting our oceans, lest we lose things forever which we have not yet even discovered."

Another biologist, Susan Jewett, a specialist in fish preservation at the Smithsonian Institution in Washington, flew to Indonesia this week to supervise the final preservation of Erdmann's coelacanth.

"I would be absolutely shocked if there weren't other populations of these fish in similar areas," said Roy L. Caldwell, chairman of the department of integrative biology at UC Berkeley. "We now know they live around active volcanic islands with deep caves in the seawalls that plummet straight down for hundreds of feet to a sloping bottom. So they may well be living in many other similar habitats."